In recent years, there is a demand for microminiaturization of an interconnection for higher density integration on a semiconductor device. To meet the demand, it is under consideration to use a copper (Cu) interconnection having lower electrical resistance instead of a conventional aluminum (Al) interconnection as the interconnection for the semiconductor device.
A damascene process is known as an exemplary method for forming a minute copper interconnection.
In the damascene process, for example, a first interconnection trench conformal to a predetermined interconnection pattern is first formed in a first interlevel insulating film of silicon oxide (SiO2) formed on a silicon substrate. Then, a copper film is formed over the first interlevel insulating film as filling the first interconnection trench. In turn, an unnecessary portion of the copper film present outside the first interconnection trench is removed by polishing the copper film through a chemical mechanical polishing method (CMP method), whereby a first copper interconnection is formed as embedded in the first interconnection trench. Subsequently, a second interlevel insulating film is formed over the first interlevel insulating film, and a via-hole is formed in the second interlevel insulating film as extending to the first copper interconnection. Then, a third interlevel insulating film is formed on the second interlevel insulating film having the via-hole. In turn, a second interconnection trench is formed in the third interlevel insulating film, and a second copper interconnection electrically connected to the first copper interconnection is formed in substantially the same manner as the formation of the first copper interconnection by filling the via-hole and the second interconnection trench with copper.
Copper is more diffusive into silicon oxide than aluminum. Therefore, copper is liable to diffuse into the interlevel insulating film of silicon oxide, thereby causing short circuits between interconnections.
In order to prevent copper from diffusing into the interlevel insulating film, for example, a barrier film is formed between the copper interconnection and the interlevel insulating film. Exemplary materials for the barrier film include tantalum (Ta) and tantalum nitride (TaN).
Patent Document 1: Japanese Unexamined Patent Publication No. 11-265890